The present invention relates to a crystal pulling unit for the production of a crystal block, which includes a crucible for the meltable material forming the crystal block and which further includes a recharging tube leading to the crucible to supply the meltable material in granulate form.
Crystal pulling units that are generally of the aforementioned type are known for the pulling of crystal blocks from semiconductor material using the Czochralski method. These units mostly work continuously in that during the pulling of the crystal block, the meltable material which ultimately forms the melt is constantly supplied in the form of a granulate. Reference is made to German Patent No. 2,821,481 as an example of the state of the art which is incorporated herein by reference. Comparable crystal pulling units are, however, also used for semi-continuous Czochralski pulling methods. The recharging tube is made of quartz material, as is the crucible.
While operating such crystal pulling units, one often finds that clogging occurs in the recharging tube. If that happens, the unit must be brought to a standstill, causing interruption of the process which generates relatively higher costs. Another disadvantage of known crystal pulling units lies in the fact that when finer granulate fractions impact on the liquid level of the melt in the crucible, these fractions "dance" on the liquid level, instead of melting, and in this way enter the pulling space above the melt and contaminate it.
It is therefore an object of the present invention to design a crystal pulling unit of the type discussed above in such a way that the danger of clogging in the recharging tube is as small as possible, and that fine-grain fractions are not able to pass over into the pulling space above the liquid level.